1. Field of the Invention
The invention relates to an arrangement for the hydraulic operation of a rear cover, a covering top or the like on a vehicle, with at least on double-acting hydraulic working cylinder which is connected, on the one hand, to the vehicle and, on the other hand, to the covering top and its working chambers are in connection with each one side of a switched pressure source via one check valve each, wherein both of the check valves have an mutually releasing device and each of the working chambers parallel with respect to the check valves is kept via a pre-stress valve, which steers into the tank, at a specified pressure level.
2. The Prior Art
Arrangements of that type are known and make possible, for example, the automatic operation of vehicle doors, engine hoods, maintenance caps or also of covering tops of trunks or a chamber holding a convertible top. By means of the releasable check valves, it is ensured that, in the case that the operational pressure is turned off or fails, the covering top remains hydraulically blocked in the respective position, in order to switch off uncontrolled movements and thus possibly resulting dangers. The pre-stress valve makes possible the further controlled movement of the covering top in this condition, for example, by hand, to allow for an emergency closure against the force specified by the pre-stress valve.
A disadvantage of the described known arrangement of the mentioned type is, however, the condition that, in the case that an object or a body part of a user is wedged in, the covering top or the like continues to operate until the very high pressure--and thus also very high forces--of the pressure-limiting valve is reached. This can lead to serious injuries or damages. Even in per-se known pressure-monitoring devices in the system for other hydraulic systems, for example, through monitoring of, for example, the change in the number of rotations of the pump or the like, it takes some time until the pressure increase through something being wedged is noticeable as an increase in the pressure at the site of measurement and is then shown as a change in the monitored parameter. During this time interval, an injury or damage could have already occurred.
It is the object of the present invention to improve a known arrangement of the initially mentioned type such that the described disadvantages are avoided and that, especially in a simple and safe manner, a passive wedging protection is realized.